1. Field of the Invention
The present invention relates to a vulcanization molding method for vulcanization molding a green tire and its vulcanizing machine.
2. Description of the Related Art
In, for example, a bladder type vulcanizing machine, after a green tire is charged into a mold by mold clamping, high temperature and high pressure nitrogen gas is supplied into a bladder inserted into a tire hole to expand the bladder whereby the bladder is caused to contact an inner wall surface of the tire tightly. Then by heating the nitrogen gas with a heater disposed in an agitating passage while agitating the nitrogen gas in the green tire (in the bladder), the green tire is heated at a vulcanizing temperature through the bladder and at the same time the tire is pressed in the molding direction to perform vulcanization molding (see for example Patent Reference 1).
[Patent Reference 1] Japanese Patent Laid-Open Publication No. 7-329066.
To increase the temperature of nitrogen gas to a vulcanizing temperature for short time, it is preferable to cause nitrogen to be agitated to flow at high speed with respect to a heater so that a heat is supplied to the nitrogen gas at a high heat exchange ratio. However, in the above-mentioned conventional configuration in which nitrogen gas is heated with a heater disposed in the agitating passage, after the flow rate of nitrogen gas was lowered during agitation the nitrogen gas reaches heater. Thus, it is difficult to heat nitrogen gas at a sufficiently high heat exchange ratio. Therefore, a method of compensating a lowered part of the flow rate is considered by increasing agitation ability by an agitation mechanism for example thereby to increase the flow rate of nitrogen gas. However, in this case this method leads problems of increase of the running cost for operating the agitation mechanism and of large sizing of the agitation mechanism. Further, it is also considered to increase the diameter of the heater and to mount a fin so as to increase a contact area between the heater and nitrogen gas. However, the heat capacity of the heater is also increased and a sufficient effect cannot be obtained.